Contact materials based on silver-tin oxide have proven to be particularly advantageous for use in low voltage switching apparatus of the energy technology, for example in motor contactors and also in power switches. Contact pieces of silver-tin oxide in motor contactors have a high lifetime number of operations, but have the disadvantage that, under the influence of arcing, oxide layers form on the contact surfaces which are thermally very stable leading to increased contact resistance. Therefore, when carrying continuous current in the switching apparatus, unacceptably high excess temperatures occur at the switching members which can lead, in particular, to damage at the synthetic parts.
In DE-OS No. 33 04 637, No. DE-OS 34 21 758, and DE-OS No. 34 21 759, sinter contact materials having the constitution AgSnO.sub.2 Bi.sub.2 O.sub.3 CuO are described which, on the one hand, meet the requirements made for lifetime number of operations and, on the other hand, of switching-on capacity. In these materials, a relatively high bismuth oxide fraction can be present which is introduced either via the intraoxidized alloy powder or via a separate addition of bismuth oxide to the intraoxidized alloy powder. However, these materials reach acceptable values with respect to excess temperature only if the total parts by weight of the oxide is limited to 8% to 11%.